Hmm. That’s pretty curious. I’d reach out to our technical support team: https://help.sense.com/hc/requests/new. They can take a closer look at the data and may have some ideas on why this is happening.
Thanks, Ben! Request submitted. I failed to mention in my submission that I’ve got photos of the installation, if there’s any question regarding how the CT clamps are oriented / connected, etc. Another thread in these forums seemed to suggest that clamp position / orientation could impact readings - but even that thread only mentioned a variation of 4% based on clamp placement - and I’m seeing 10% variance from what the upstream meter is reporting.
Quick question - are you looking at instantaneous power (Current Usage) from the Eagle vs. the Power Meter/Bubble power readings ? Or are you looking at energy ? I have both the the Eagle and a Sense, though my setup is a little different since I have solar as well. But the thing that I have discovered is that the Eagle/meter sample rate is much slower, even in the fast poll mode, than the Sense. I haven’t been able to to figure out via Eagle documentation whether the Current Usage number is the highest power point during the entire poll period, or merely a sample at a fixed interval. If it is the highest value during the poll period, then that could explain the differential. My experience is that the energy numbers (integral of power over time) correlate quite closely between the Sense and the Eagle, but looking over time weighs against discrepancies when the power usage is small - relative accuracy at higher power levels swamps poorer accuracy at low power usage.
What is the claimed accuracy of the Sense CT clamps??? A good LEM CT will be accurate to 0.5 percent or better. Can we get the data sheet on the Sense CT?? What company is making the CT clamps for Sense??
Unfortunately I don’t have a data sheet on our CTs I can share at the moment (although we are certainly open to it). Our CTs are accurate to 0.5% and likely more accurate than that, as we custom make and calibrate our CTs to reduce inaccuracy. Since you’re interested, and it’s an interesting question, we’re going to write a blog post on the topic with a little more information.
will you give us a nudge when the blog goes up? I’m curious as well
yes I’m interested because my career in the USAF was in Metrology.
Just to pinch in my two cents. My local utility, PG&E, makes total kwh usage available online after a day of two.
I’ve compared sense and the utility’s for a week and it was 99% accurate.
39kwh, vs 39.1 sense reported
85 vs 84.9
And so on
I just received my first bill since installing my Sense. I have a spreadsheet where I entered every hourly, daily, weekly reading from Sense. I compared the reads with my utility and find my Sense to be extremely accurate. I was billed for 746 kWh and Sense calculated 744.7 kWh. That’s 99.83% accurate. I love it.
My electric provider uses SmartHub so I can compare my electric use to Sense and both are matching very closely so far which I was happy to see.
Thanks to the new Sense export capabilities I was able to do an hour-by-hour accuracy analysis of Sense since the start of 2018. It looks really good. I can pretty much count on it being within 2% of my net meter reading. Just watch out for the hours when the monitor is offline due to networking issue. Details here:
We’re seeing sense estimates of Solar to be about 5% less than what our SolarEdge inverter is reporting (measured in kWh on any given day).
That’s in line with what I was seeing in my more detailed analysis here - Sense energy is 3-4% below my SolarEdger inverter.
I have seen various tidbits around the web that suggest that SolarEdge’s are very accurate with respect to instantaneous power measurements, but run a little high when looking at energy calculations.
Way back when, I was comparing my SolarEdge, with my meter, with Sense. At the time, the SolarEdge inverter was reporting 3% higher than my meter, which was reporting 3% higher than Sense. That’s how we first identified the “Daytime Dip,” which was eventually tracked down to a faulty calibration process and a fix was sent out to all units.
Since then, my solar has been more or less spot on with my meter, while my SolarEdge is…still 3% higher than my meter. Gee, why would an inverter company want you to believe you were making more energy than you actually were? Alternatively, why would a utility want you to believe you were making less energy than you actually were?
I think the inverter and associated feed wires are the guilty parties. Why ?
- I see it frequently on solar sites like this one:
Lot of speculation on where the difference comes from. Voltage drop losses, power feeding the SolarEdge, etc.
- I can spot an easy 1% difference between the inverter and Sense in voltage readings. When my SolarEdge reads 245.3V, I see only 121.2 and 121.4 (242.6V total) on my mains. Voltage readings, even AC should be pretty close to spot on, so I attribute that to the voltage drop between the SolarEdge measurement point and the Sense breaker.
I notice your Sense monitor was clipping the bottom (Assume Solar). You might check out the Beta group and the release they have for the meter. It displays the full range (including negative). You must request access to the Beta version.
Of course not me as im just a lurker.
Check out Support@sense.com if interested.
The only time my Sense data has gone negative and was clipped below zero, as you describe, was when I had some weird Sense monitor problems in the past that have actually caused negative Total Usage and Solar Production. But when everything is working fine, all the traces are positive in the graph (solar is really negative energy usage but it shows positive in Sense). The negative-going part of the Rainforest Automation “Demand” graph reflects my net usage (Total Usage minus Solar), not the same as Sense’s “Total Usage”.
I’ll use your suggestion if I see negative clipping again - I would be helpful.
I get negative a lot. That’s because I have several things connected to the same panel that is on my solar sub panel. When my car is charging at night I get a negative number.
I wondered the same about the “Totals” accuracy and they don’t
seem to match everywhere.
But I’ll show you where I think it does a fairly good job. It’s
the “Trends” page and specifically the “Usage” stats.
I’m attaching my usage from this page for yesterday and also the
text message I got from the power company this morning showing
Sense put it at 136
power company at 144
That’s a difference of 8 KWH. My price for electricity is $0.085
I think that’s pretty close and is a 68 cent difference on a day when
we had below zero temps and usage was extremely high.
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